1. Field of the Invention
Frosts are a mayor problem during spring time because this is the time when crops are more vulnerable.
There are two different types of frost: radiative frost, and advective freeze. The former is produced when the earth looses heat during clear nights. It is the inverse process to the earth heating during the day by solar radiation. In this case is the earth what irradiates heat to the atmosphere. The air is getting colder from the bottom to the top very slowly. Therefore lower air layers have less temperature than upper layers. Hence people talk about thermal inversion layer, which is placed at about ten meters (thirty feet) from the ground, and thirty meters thick. It is 5.degree. C. hotter than the ground level temperature. Over this layer temperature decreases again. The latter, advective freeze, occurs when a mass of cold air, or polar air comes to the crop or orchard.
2. Description of Related Art
Mankind has looked for how to fight frost effects. The most common are the use of firewood, fuel heaters, wind mills or propellers, the use of helicopters flying over the orchards, etc.
The heaters are very effective to control frosts, but they have the inconvenient of their high operation cost, because of the great fuel consumption since they are very inefficient. They heat the air to very high temperatures, which goes up quickly causing the "chimney effect". Thus, we have no radiative effect to the surrounding air. Great fuel consumption is required and great contamination is produced as well.
The other systems are the helicopters and the propellers. They both blow hotter air from the inversion layer and then this hot air is mixed with the colder air from down below, closer to the ground.
Besides these systems, I know about a patented system in Uruguay, thought to protect citrus plantations. This system is also based on the idea of taking hotter air from the inversion layer, using a ten meters high or over funnel, that has a fan on its bottom part by which cold air passes through and makes hotter air to come down to crop or orchard.
I knew also about a grower from the El Olivar county who has used an axial fan belonging to a turbo atomizer to which he put a heater in order to blow hot air to his vineyards. He abandoned this idea due to the area under control was too little. I tried something similar about five years ago with no useful results.
I have the information also of the patent appliance No. 682-94, in which the use of a moving machine that blows hot air transported by a tractor is told. The grower talks about the drawings but they were never showed. He also tells about a fan in which one can modify the angle of attack of its blades. Therefore it is clear that it is an axial fan, similar to the one the grower from El Olivar used, and the one I used before in my first experiences as well.
With the development of new irrigation techniques, sprinklers are being used to wet the crop we want to protect. But the problem now is that in some cases is not convenient to wet the crop or the tree for potential fungal diseases or some times we might have no enough water at this time of the year (winter time).
I have searched in the CAB Abstracts system, at Universidad Catolica, finding 147 articles under the command "frost protection". Only two of them mentioned something about an specific device to control frost. It was published in 1991, in "Tractory-i-Sel' skokhosyainestevennye-Mashiny" in the Russian republic of Georgia. It talks about a stationary machine, the YOP-2 and the YOP-2M which is movable.
The former is a machine placed on a tower, which blows hot air through a rotating tube of 1 meter diameter, covering a 200 meters radius area. This system has an advantage over the traditional fans or propellers, which are no effective in advective frosts (freeze). This movable machine goes over a cart and it produces fog that throws over the field. With this purpose it uses 90 to 100 MT of water per hectare.
These systems explained above are absolutely different from mine.